1. Field of the Invention
The present invention relates to a power steering device installed on a vehicle.
2. Description of the Background Art
A power steering device of the background art is shown in FIG. 9, which includes a power assisting cylinder 3 arranged between a steering shaft 1 and a chassis frame 2, a control valve 4 operated by the steering shaft 1 to control the power assisting cylinder 3, an oil pump 5 for pressurizing the operating oil supplied to the power assisting cylinder 3, and an oil tank 6 for storing the operating oil. The oil pump 5, the oil tank 6 and the control valve 4 are connected to each other through three oil pipes 7. In addition, the steering shaft 1 is provided with a spool lever 8 for operating the control valve 4, and a center arm 9 oscillated by the power assisting cylinder 3.
The background art power steering device constituted as described above is operated such that when the steering shaft 1 is turned in any of the rightward or leftward direction, the control valve 4 is operated by the spool lever 8, so that operating oil is supplied to the power assisting cylinder 3. Then, the center arm 9 is oscillated in the turning direction of the steering shaft 1 under an operation of the power-assisting cylinder 3, and the operating force of the steering shaft 1 is reduced.
In the aforesaid background art, the power assisting cylinder and the control valve 4 are arranged at a side of the steering shaft 1, and they are connected to the steering shaft 1 by the spool lever 8 and the center arm 9, so that the background art has a problem that the entire system becomes large in size and a certain accuracy is required in connecting each of the component parts, as well as the assembling work involved.
The present invention has been invented in view of the problems found in the background art, and it is an object of the present invention to provide a power steering device which saves space and is easy to assemble.
The power steering device of the present invention is installed between a steering shaft rotatably installed at a chassis frame and a steering wheel connected to the steering shaft. The power steering device comprises a cylindrical holder coaxially arranged on the steering shaft, a cylindrical rotary cylinder coaxially and rotatably installed in this holder and forming two oil chambers spaced apart in a circumferential direction between it and an inner surface of the holder, and a spool changing-over member coaxially and rotatably inserted in the rotary cylinder and connected to the steering wheel.
The holder is provided with an operating oil supply hole and an operating oil discharging hole. The rotary cylinder is formed with a pair of communicating holes between each of the oil chambers and an inside of the rotary cylinder. The spool changing-over member is formed with operating oil passages where a space part between it and an inner circumferential surface of the rotary cylinder is divided into two segments in a circumferential direction and connected with the supply holes and discharging holes. A pair of partition walls are provided for changing-over a communicating state between the pair of operating oil passages and the pair of communicating holes under relative rotation with the rotary cylinder.
The power steering device of the present invention is characterized in that the both operating oil passages are connected with the spool changing-over member, and there is provided a check valve for preventing a flow of operating oil directed from the operating oil passages connected with the supply hole for the operating oil and directed toward the operating oil passage connected with the discharging hole for the operating oil.
The power steering device of the present invention is characterized in that there is provided between the rotary cylinder and the spool changing-over member a differential mechanism for integrally rotating the rotary cylinder and the spool changing-over member, when a steering force applied to the steering shaft is low, and when the steering force is larger than a predetermined value in a case of allowing a relative rotation between the rotary cylinder and the spool changing-over member.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.